As a display apparatus, an organic light-emitting diode (OLED) is self-luminous, has a high contrast ratio, and has a wide color gamut. Besides these advantages, OLED has a simple manufacturing process, has a low power consumption, and is easy to realize flexible display. Thus, OLED becomes an important light-emitting element in a new flat panel display apparatus.
For the pixels of OLED display panel, each pixel includes a driving transistor. In an organic light-emitting diode pixel circuit, a current flowing though the OLED is not only controlled by a data signal Vdata, but also affected by a threshold voltage Vth of the driving transistor.
In different pixel circuits, characteristics such as the threshold voltage and carrier mobility of the TFT are different from each other, and the driving transistor included in each OLED pixel circuit cannot have exactly same performance parameters. Thus, currents flowing through the OLEDs may be different caused by a threshold voltage shift (Vth Shift) in the driving transistor. This may finally cause adverse effect to the luminance uniformity and constant brightness of the organic light-emitting diode display apparatus, and accordingly adversely affects a display effect of the organic light-emitting diode display apparatus.
With consideration of the above-described points, it is necessary to provide a threshold voltage compensation circuit to the pixel circuit in order to avoid the adverse effect caused by the threshold voltage shift to the luminance uniformity and constant brightness of the organic light-emitting diode display apparatus.
Usually, a threshold voltage compensation circuit may output a charging signal to a capacitor during a charging stage in order to charge the capacitor so that the capacitor can maintain a voltage of the gate electrode of the driving transistor during the light-emitting stage. With this configuration, the current flowing through OLED can be controlled to have no relation to the threshold voltage Vth of the driving transistor.
However, in the driving circuit according to the prior art, in some cases, a design of the data signal is restricted by the power source, and this may lower a design flexibility.